Generally, a fuel cell is an energy conversion device that generates electrical energy through an electrochemical reaction between a fuel and an oxidizer and has an advantage that power can be consistently generated as long as the fuel is continuously supplied.
A polymer electrolyte membrane fuel cell (PEMFC), which uses a polymer membrane capable of permeating hydrogen ions as an electrolyte, has a low operating temperature of about 100° C. or lower as compared to other types of fuel cells, and has advantages of high energy conversion efficiency, high output density and fast response characteristics. Besides, since it can be miniaturized, it can be provided as portable, vehicle and household power supplies.
The polymer electrolyte fuel cell stack may comprise a membrane-electrode assembly (MEA) having an electrode layer formed by applying an anode and a cathode, respectively, around an electrolyte membrane composed of a polymer material, a gas diffusion layer (GDL) serving to distribute reaction gases evenly over reaction zones and to transfer electrons generated by oxidation reaction of the anode electrode toward the cathode electrode, a separating plate (bipolar plate) for supplying the reaction gases to the gas diffusion layer and discharging water generated by the electrochemical reaction to the outside, and a rubber material gasket having elasticity disposed on the outer circumference of the reaction zone of the separating plate or the membrane-electrode assembly to prevent leakage of the reaction gases and the cooling water.
Conventional separators for a fuel cell stack are configured such that the flows of the reaction gas and the resulting water travel in the same direction through two-dimensional channels or are distributed and discharged through intersecting three-dimensional solid shapes. However, they have a structure that is not suitable for efficiently discharging a variable amount of water under various operation conditions, thereby having a problem of deteriorating the performance of the fuel cell stack.
Particularly, there is a technical problem that a water transfer (supply/generation/discharge) imbalance in the fuel cell occurs in the high output region and a high mass transfer resistance (usually diffusion resistance) of the reaction gas in the reaction surface occurs.
In addition, in the case of conventional separating plates, for example, separating plates applied by metal mesh, expanded metal, etc., transfer passages of the reaction gas and the generated water are not distinguished clearly, thereby resulting in problems of reduction in the reaction gas supply efficiency and performance instability due to the condensed water occlusion in the microchannel.